Behavior Of The Fire Resistance Of Angle Steel Strengthened Reinforced Concrete(RC) Beams Considering Twice Loading

The transformation and maintenance of the building is an important way to solve the safety,applicability and durability of the reinforced concrete structure.Having little change of the structure of the original shape,effective improvement of the bearing capacity and ductility,economical and easily applied,Angle steel strengthening method is widely used in various engineering reinforcement.Because the angle-steel close to the outer space of the strengthening member,it is easy to be affected by high temperature under fire.At the same time,as the reinforcement component,the secondary load can not be ignored.Based on the experiment on the fire resistance test of RC beams strengthened with angle steel in our research team,this article will continute to analysis the angle steel strengthened RC(ASSRC)beam,in which the secondary load effect was considered.The main researches are as follows:The finite element analysis temperature field model and two different conditions of ASSRC beams coupled thermos and mechanical finite element analysis model are established by ABAQUS software,the applicability of these model are verified by experimental data.The "Kill-Activate" and "Element Tracking" ABAQUS method was used to establish " the secondary load effect " finite element analysis model,by comparison of different first load levels and comparison of different load ratio analysis,summed up the fire resistance of ASSRC beams in consideration of secondary load.The results show that: When the load ratio is small,the secondary load have a little influence of the ASSRC beam in the process of fire,but as the load ratio increases,under thermo mechanical coupling,the effect of secondary load on structure is more obvious;The first load level of the strengthened beam has limited influence on fire resistance.In this article,the compressive strength of concrete,yield strength of Longitudinal reinforcement,diameter of longitudinal reinforcement,yield strength of angel steel,the thickness and width of angel steel,load ratio,the thickness of the protective layer,the thickness of plate floor,bolt rod strength and bolt spacing,a total of 11 parameters were analyzed to get the influence of the parameters of fire resistance performance of ASSRC beam.The results show that: the load ratio and the thickness of the protective layer are the two most importance factors of the fire resistance of ASSRC;bolt rod strength,bolt spacing and the thickness of angel steel have small effect on the fire resistance;the other parameters have varying degrees of impact on the ASSRC beams.